Athletic fields such as baseball fields, softball fields, soccer fields and football fields are subject to extraordinary demands. Heavy foot traffic, play during inclement weather and overuse lead to problems in effective field management. Additionally, the poor physical structure of soils (native and imported), improper construction techniques and improper maintenance magnify problems caused by these factors.
The most common problem in baseball and softball field maintenance is providing a skinned infield surface that is playable in all weather conditions. Furthermore, due to budget and manpower constraints, these infields must be easy to maintain. More than 80 percent of all activity during a game takes place in this area.
The majority of infields are constructed using a soil mix comprising sand, silt and clay. The percentages of sand, silt and clay in an infield mix varies across the world based on local soil sources. No standard exists for major league baseball or for softball.
Desirable characteristics for playability include the following: a smooth, level surface for running, sliding and fielding balls; a loose, friable surface having between 1/4 inch and 1/2 inch of loose surface material that provides a cushioned surface for ball hops, running and sliding, and which exhibits relative freedom from skin abrasion due to sliding contact with the surface; a surface that does not become slippery when wet, i.e., one which can absorb light rains and provide surface drainage during heavy rains; a surface that drains well and dries out quickly in wet weather; a surface that does not dry, become hard, and crack during the hot summer months, i.e., a surface capable of retaining minimum moisture levels; a surface that is easy to scarify using a nail drag or other implement that reduces surface compaction.
During the last 30 years, an industry has developed which provides groundskeepers and coaches with materials and tools that help make infields playable. Universities and private industry have invested substantial amounts of money and time in attempting to understand infield maintenance and construction. Recently, governing bodies have been created in an attempt to standardize practices and to provide recommendations to groundskeepers and coaches.
The most common method of improving a skinned infield is to modify and top dress infield soils with amendments that absorb moisture and help the field remain loose and friable. There are several objectives to adding amendments to infields. Some products are more effective than others in meeting these objectives.
Common among the objectives are the following.
1. Mixed into the top 4 to 6 inches of skinned soil, the amendments absorb rain and other moisture from infield soils so that the field does not become muddy during rainy days.
2. Mixed into the top 4 to 6 inches of skinned infield soil, the amendments help prevent compaction by preventing infield soils from binding together.
3. Used as a light surface top dress, they provide a loose, level, smooth playing surface.
4. Used as a surface top dress, the amendments provide a loose surface suitable for diving and sliding into bases.
5. The amendments retain moisture during hot summer months to keep a field from drying out and becoming hard and difficult to maintain, while encouraging drainage.
6. They provide a brown to red color that gives a field a "major league" appearance.
Amendments which have been tried in the past include sand, cat litter, oil and grease absorbents, calcined diatomaceous earth and crushed aggregates including brick, limestone, sandstone, shale, etc. There are several properties that differentiate amendments. They include particle sizes, moisture absorption capability, color, and physical stability.
Sand has not proved to be an acceptable amendment in most cases. Because of its small particle size, at least 80 percent by weight of sand must be present in a soil structure to keep that soil from becoming compacted. Amounts less than 80 percent actually encourage compaction since the sand fills available pore space in the soil. Other properties that make sand less desirable include its negligible water absorption and retention capacity. While soils containing very high sand content generally drain rapidly, there are no pores to retain the residual moisture necessary to obtain optimum playability, especially during hot summer months.
Cat litter was one of the first materials tried by groundskeepers to absorb moisture on infields following a rain. Cat litter is a dried clay containing substantial amounts of sodium and/or magnesium bentonites or other clays which may exhibit massive swelling in the presence of water. Although these products absorb water, the water causes rehydration of the dried clay, which breaks down quickly into a wet clayey mass. It can be used effectively only one time to absorb moisture, and if used often, can produce a surface which is slippery when wet, and which contributes to poor drainage by clogging intergranular drainage passages. Because it breaks down easily, it is not used for top dressing infields to provide a consistent surface.
Oil and grease absorbents are similar to cat litter in that they are manufactured to absorb liquids one time. Oil and grease absorbents have a very wide particle size distribution and also rehydrate into a wet clay.
Materials such as calcined diatomaceous earth, many crushed sandstones, crushed limestone, and similar white or light-colored materials have seen little acceptance as soil amendments for skinned sports fields. None of these materials due to their color, are acceptable as top dressing. In addition, calcined diatomaceous earth is brittle, and rapidly breaks down. Crushed brick and shale have been touted as amendments, but have been found to contribute to cuts and abrasion during sliding. Crushed brick, additionally, does not have the desired porosity. Both crushed brick and shale have been shown to decrease soil drainage.
Ceramic aggregates used as heavy duty oil and grease absorbents offer some of the desirable characteristics for a soil amendment material. However, the color of most of these products is not suited for infields. Moreover, when used as top dressing, these materials have been shown not to perform satisfactorily. A brown to red colored product of the assignee of the present invention has achieved success as a soil amendment for skinned sports fields. However, playing performance and application performance are still in need of improvement.
It would be desirable to provide to the industry a porous amendment which is inexpensive, which promotes rapid drainage while exhibiting considerable water retention, which is of a uniform and acceptable red-brown color, which exhibits playing characteristics which render the amendment suitable not only as a below-surface additive, but for top dressing as well, which is non-swelling, and which is stable, i.e., resisting both physical and chemical break down, and in particular, hydration to fine clayey materials.